Which of the following is not a threat to coral reefs?

answer:

coral

step-by-step explanation:

coral reefs don't hurt themselves

answer: planting trees

reduce your carbon footprint.

using   less

using organic fertilizer to avoid chemicals running into the ecosystem.

i guess these are some ways that are not harmful to coral reefs : =)

step-by-step explanation:

compare

, and

for

step-by-step explanation:

we can analyze the pattern at which the terms increase. let us denote , , , so that we can call

note the following:

the pattern: to get the next term value, we just add the next term number (e.g. 1st, 2nd, to the previous term value (term values are the given numbers in the question, 1, 3, 6, 10, 15,

from , to get to , we add

from , to get to , we add

etc.

we need to form a recursive formula, a formula that has the next term as a function of the previous term. so a possible recursive formula can be

, and for